upas/common: delete library on 'mk clean'

libcommon.a$O doesn't end with a .a, so mk
doesn't know how to look inside it in order
to check if the files are up to date.

This means that when 'mk clean' is run,
libcommon.a$O looks up to date:

	% mk clean
	...
	% mk
	mk: 'default' is up to date

Deleting the library works around this problem.

0 files changed, 0 insertions, 0 deletions